1. Field of the Invention
The invention relates to a tubular mould for the continuous casting of round and polygonal billet and bloom cross-sections according to the precharacterising clause of claim 1 or 2.
2. Description of Related Art
In the continuous casting of steel in billet and small bloom cross-sections, tubular moulds are used. Such tubular moulds comprise a copper tube fitted into a water jacket. In order to achieve circulation cooling with a high flow rate of the cooling water, a tubular displacer is arranged outside the copper tube with a small gap relative to the copper tube. The cooling water is forced through between the displacer and the copper tube over the entire circumference of the copper tube at a high pressure and high flow rate of up to 10 m/s and above. To prevent any damaging deformations of the copper tube during casting operation due to the high temperature differences between the mould cavity side and the cooling water side, the copper tubes, which are essentially held only at the lower and upper tube end by flanges, must have a minimum wall thickness. This minimum wall thickness is dependent on the casting format and is between 8 and 15 mm.
Since the beginning of industrial continuous casting, efforts have been made by those skilled in the art to increase the casting speed in order to achieve higher outputs per strand. The increase of the casting capacity is closely related to the cooling capacity of the mould. The cooling capacity of a mould wall or of the entire mould cavity is influenced by many factors. Important factors are the thermal conductivity of the copper tube, the wall thickness of the mould wall, the dimensional stability of the mould cavity in order to avoid distortion or air gaps between the strand skin and the mould wall, etc.
However, besides the cooling capacity, which may exert a direct influence on the output per strand for a given strand format, the service life of the mould also constitutes an important cost factor for the economic efficiency of the continuous casting plant. The service life of a mould expresses how many tonnes of steel can be cast into a mould before wear phenomena in the mould cavity, such as abrasive wear, material damage, in particular hot cracks, or damaging deformations of the mould cavity, necessitate a change of mould. Depending on the state of wear, the mould tube has to be scrapped or undergo refinishing so that it can be used again. In the case of standard conical moulds, moulds with somewhat greater copper tube wall thicknesses have higher dimensional stabilities.